She hated that she had actually cheated on Clark on his birthday,
But does it really count if she cheats on Clark with Clark.
of all days, despite the fact that the man with whom she had cheated on him was Clark himself.
You know, this is one aspect of the love triangle built for two they never really expored in canon. I have to say though this is much preferable to Scardino being a distraction.
Sure, she could also argue that it technically wasn’t Clark’s actual birthday, but the birthday of the Kents’ child.
But it is his birthday. I guess she does not know that.
Who knew when Clark’s real birthday was, or if Krypton’s calendar years were even in the ballpark of Earth’s or calculated in the same way, since it didn’t circle around this sun? None of those facts eased her guilt any.

that Lois does not know more of Clark's background.
Today was the date Clark had chosen as his birthday when he arrived on Earth,
I don't think this is true on any level. Although the choice of this day is somewhat arbitary, it's not likely the Kent's could be exact on his age, it was not him who chose it. On the other hand, when he arrived on this earth, it was already chosen for him.
She should have remembered it was Clark’s birthday and mentioned it to him the night before as another reason for him to kick Cat out of his apartment and let her stay.

not going to have that horrible conversation yet.

more kissing. I am getting in the last chances to be glad before it ends for a long time.
“What? You thought I forgot?” she teased, heading into her bedroom.
Lois:Just because I have not wished you happy birthday yet, despite having already seen you today, does not mean I forgot.
Lois to herself:OK, maybe during the three times I saw him earlier today I was not thinking it was his birthday, but still.
You were the one with amnesia, Chuck, not me.”

I like her humor. Plus

she is calling him Chuck.
She left the big wrapped gift inside and took out the smaller one.

she got him two gifts.
The big gift could wait until after she finished her investigation.
Now I am really going to have to stick with this story to find up what the big gift is. OK, I doubt I would ever give up on the story, but there is lots more suspense now.
She knew she couldn’t make love to Clark tonight, and then tell him they needed to slow down their relationship tomorrow.
Yep, somehow I doubt she would be able to give up on being with Clark after that.
Not only would he think that she really didn’t love him and was only after his body,
That would only happen if she could will herself to do such a thing.
but she didn’t think she would have the inner strength to do that to herself, let alone him.[Quote]
Or that much resolve to not be with Clark in that way once she had experienced it. OK, maybe she has that much resolve. The emotional weight on both of them would be horrendous.
[Quote]“Yes.” Clark flushed. “I mean, thank you.”
At least he managed to thank her. For a bit I was afraid he would lead into his rejecting her speech.
“That’s better. It’s not much, but…” She shrugged. “I wanted to get you a tracking bug, so you’d know that I would always know where you had run off to, but I didn’t have time to get it.”
His eyes opened wide and he gulped.

more kissing. I guess my expectation of no kissing for a while was premature.